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When Michelle Obama took up residence in the White House four years ago, she became not only the first lady of the United States, but also the first lady of American fashion. Check out her style evolution. (Published Thursday, Apr 24, 2014)

Updated at 7:22 AM EST on Friday, Jan 25, 2013

When Michelle Obama stepped out beside her husband on Inauguration Day, all eyes — at first — were on what she was wearing.

Her outfit for the occasion: A navy dress and coat ensemble by designer Thom Browne, in a fabric based on the style of a silk necktie. A necklace by designer Cathy Waterman and a belt and shoes by J.Crew. Ahead of the big event, Obama made headlines for the new bangs she debuted.

Michelle Obama Style Guide

The White House also revealed the Obama daughters' outfits: Malia wore a J. Crew ensemble and Sasha a Kate Spade coat and dress.

Monday marked the start of a new term for President Barack Obama — and another four years of fashion influence and scrutiny for Michelle Obama. And if a look back at the first lady's style choices during her husband's first term is any indication, she’s totally fine with both.

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"What has become part of the first lady's job is to act as a champion of American fashion," says Kathleen Graddy, curator of the First Ladies Collection at the Smithsonian’s National Museum of American History, where Michelle Obama's Jason Wu gown from her husband's 2009 inauguration is now a permanent fixture. Following the second inauguration, Obama's outfit and accompanying accessories will be placed with the National Archives, NBC News reported.

"Michelle Obama does a laudable job of showcasing a variety of different designers. It's certainly a place where the nation, and the world, gets to see the work of our designers and the fashion industry," Graddy said.

Unlike her predecessors, Mrs. Obama has not just showcased homegrown talent but has also fundamentally changed the way Americans view the nation’s first wardrobe.

"More than anything else, she broke that first lady uniform that we had gotten so used to seeing," In Style editor-at-large Hal Rubenstein says.

"How a first lady dressed – an image that was basically fostered by Nancy Reagan, and you can even add Hillary Clinton to that, where you wore this tasteful wool bouclé suit or dressed in a gown – was elegant and modest. There was never a hint of sex appeal anywhere," he noted.

But Michelle Obama’s fashion hallmarks — exposed arms, cinched waists, a mix of high-end (Azzedine Alaïa, Alexander McQueen) and mass-market (J.Crew, Target) brands and tailoring that highlights rather than hides her curves — have split from that tradition and made her one of the most watched women in the world.

"Look at all the White House first lady portraits. They are all wearing that suit. The first official portrait of Michelle Obama was in a black, sleeveless Michael Kors sheath, and the reaction was, 'Oh, look, here’s a modern American woman.' Here’s a woman who the cool women who work in New York or Los Angeles – or anywhere for that matter – would like to be represented by," Rubenstein added.

"In terms of her regular workday wardrobe, an American woman can look at that and think, 'I’d love to buy a dress like that,' or 'I’d love to try a shape like that,' instead of looking at a first lady and thinking ‘Oh, that’s her uniform.’”

"There are very few people that hold the country's attention the way she does. I don't think anyone ever noticed what Hillary Clinton wore, or necessarily cared," Lyons told Style.com in 2010.

"I love that [Michelle Obama] wore an Alaïa dress with a J.Crew cardigan and Jimmy Choo shoes. And she shops her closet. I'll notice sometimes she’s worn something of ours and then it’ll be altered — she’s actually had it changed, which I think is kind of amazing — and she’ll wear it completely differently. It says a lot about what works today," she said.

It’s a conundrum all first ladies face: how to be true to their own sense of style while operating within the confines of public and political expectations.

"First ladies prefer to concentrate on their work rather than on their wardrobe," Smithsonian curator Graddy said. "They are happy to supply that information [about which designers created their outfits], and they want to look appropriate — that’s part of their job, too — but they don’t want it to be the primary focus of their job."

For Michelle Obama, her wardrobe can aid in her work.

During her husband's presidency, she has drawn attention to childhood obesity and placed healthy eating habits firmly at the forefront of her public agenda. That she unapologetically looks great, and like she enjoys fashion, makes her more relatable to the average American and helps her message to stick.

"She didn’t move to Washington and become part of this paradigm of how Washington people should dress. You see her out on the lawn with her kids, or she’s coming to visit schools, and she is wearing a twin set or a J.Crew top — or she goes on 'The View' in a dress that she bought at Target," In Style's Rubenstein added.

The fact that the first lady doesn't favor a particular brand, designer or price point has boosted her appeal and sent a helpful message to American women, too, said Rubenstein.

It has also boosted the fortunes of the American fashion industry.

In a 2010 study of her economic impact, David Yermack of the New York University's Stern School looked at 29 clothing companies whose garments Michelle Obama wore in 189 public appearances between November 2008 and December 2009. His study found that a brand's stock price typically jumped by 2 to 3 percent after she wore its label — and that the overall value to a company of Mrs. Obama making an appearance in its brand could reach $14 million.

Designer Naeem Khan discovered first-hand just how influential Mrs. Obama can be when she wore one of his outfits to a state dinner in February 2009. These days, a quick glance at the many actresses who wore his gowns to the Golden Globe Awards this month is testament to the first lady's influence.

It’s unlikely we’ll witness a major change in her style, despite her new hairstyle. Rather than make radical wardrobe turnabouts, she focuses on a few surefire silhouettes and experiments with color, designers and accessories.

Rubenstein explained her style: "Very tailored clothes. You’ll never see her wear a skirt that is too short. She likes to show her waist. She tends toward florals, and she likes strong colors without being neon. She rarely, if ever, wears stripes. She likes to show off her arms. She doesn't wear a plunging neckline or a backless dress, because that would get her in too much trouble."

As for her inauguration wardrobe? Until Monday morning, that was anybody’s guess — and that’s just how her fashion followers wanted it.